2. Field of the Invention
This invention pertains to heavy-duty, friction type bearings.
More specifically, this invention pertains to friction bearings utilized in sealed bearing roller cone rock bits.
The bearings of roller cone rock bits typically carry heavy loads (up to 40,000 pounds), plus intense and continuous shock loads during bit operation. Relative sliding velocities between the cone bearing surface and its associated journal bearing run from fifty to as much as five hundred surface feet per minute. Lubrication is typically limited to self-contained noncirculating grease and bit operating temperatures, run between 150.degree. and 400.degree. Fahrenheit.
3. Description of the Prior Art
In the past, many materials and material systems have been used in the production of friction bearings for roller cone rock bits.
U.S. Pat. No. 3,721,307, for instance, specifies the use of beryllium copper in a rock bit bearing. Porous steel bearings produced from powdered metal and containing lubricants, such as graphite, in their interstices are described in U.S. Pat. No. 4,105,263. Bearings wherein the steel members are treated to produce a special surface are also well known in the art. For example, U.S. Pat. No. 4,012,238 describes a treatment involving the combined use of boronizing and carburizing to produce a hardened "case" which is used as a bearing surface. U.S. Pat. No. 3,995,917, assigned to the same assignee as the present invention, describes the use of aluminum bronze in the production of a rock bit friction bearing. Tungsten carbides have also been used, as have stellite and other hard materials which are applied by metallurgical hardfacing methods.
The useful life expectancy of these various systems varies according to the particular drilling conditions under which they are used but are typically about 100 hours. Depending upon these conditions, lifetimes of from 20 hours to about 150 hours are common.